What does 回線 mean?
回線 is a Japanese noun meaning “circuit; line” in English. It is written as 回線 in kanji, かいせん in hiragana, and kaisen in romaji. This word is part of JLPT N1 vocabulary.
Example sentence
この回線の細さじゃ、動画は見られないよ。
This connection is too slow for me to watch movies.